The present invention relates to a new process for the preparation of 4,5-allene ketones by the Saucy-Marbet reaction by reacting tertiary propargyl alcohols with alkenyl ethers in the presence of aliphatic sulfonic acids or sulfonic acid salts. The 4,5-allene ketones formed as a result can be converted in a manner known per se into 3,5-diene ketones by a subsequent isomerization or into saturated ketones by a subsequent hydrogenation. A number of 4,5-allene ketones, 3,5-dienones and the corresponding saturated ketones are valuable intermediate products for the preparation of vitamin E, A, K1 and carotenoids.
A process for the preparation of 4,5-allene ketones by reaction of propargyl alcohols with alkenyl ethers in the presence of an acid catalyst is described in U.S. Pat. No. 3,029,287 and from the publication by R. Marbet and G. Saucy, Helv. Chim. Acta (1967), 50, 1158-1167. p-Toluenesulfonic acid is mentioned in these as a particularly suitable acid catalyst. However, the reaction times necessary to achieve a complete conversion of the tertiary propargyl alcohol are longer than 15 hours. In an industrial process, these long reaction times cause large reaction volumes and high investment costs.
According to EP 0 902 001 A1, 4,5-allene ketones are prepared by reaction of propargyl alcohols with alkenyl ethers at elevated temperature and pressure in the presence of KHSO4, ketals being formed. The resulting ketal can be recycled back into the alkenyl ether. For this reaction with propine or allene or mixtures thereof in the gas phase at elevated temperature, a heterogeneous catalyst comprising a zinc silicate which is amorphous to X-rays is necessary, which limits the profitability of the process.
Accordingly, an object of the present invention is to improve the space-time yield in the reaction between tertiary propargyl alcohols with alkenyl ethers and thereby achieving good yields.
It has now been found that aliphatic sulfonic acids and sulfonic acid salts catalyze the reaction of tertiary propargyl alcohols with alkenyl ethers very selectively, the reaction times for achieving good yields being shortened.
The above and other objects of the invention can be achieved by a process for the preparation of 4,5-allene ketones of the formula I 
In which
R1 and R2 represent hydrogen, saturated or unsaturated, branched or unbranched C1 to C20- alkyl, aryl or alkylaryl, it also being possible for R1 and R2 together to form a 5- or 6-membered ring,
R3 and R5 represent hydrogen or C1 to C4-alkyl and
R4 represents C1 to C4 alkyl,
by reacting a tertiary propargyl alcohol of the formula II 
in which R1, R2 and R3 have the abovementioned meaning, with an alkenyl alkyl ether of the formula III 
in which R4, R5 have the abovementioned meaning, R6 represents C1 to C4 alkyl
or a ketal of the form IV 
in which
R4, R5 and R6 have the abovementioned meaning, at temperatures of 40 to 200xc2x0 C. without a solvent or in an inert organic solvent in the atmosphere or under a pressure of up to 100 bar in the presence of an aliphatic sulfonic acid of the formula V
R7SO3Hxe2x80x83xe2x80x83V
in which
R7 represents halogen, branched or unbranched, optionally halogen-substituted alkyl having 1 to 20 C atoms or cycloalkyl,
or in the presence of a sulfonic acid salt of the formula VI
R8SO3Mxe2x80x83xe2x80x83VI
in which
R8=R7 and additionally represents aryl or substituted aryl and
M represents a cation of an organic or inorganic base.
Preferred starting materials of the formula II are, above all, tertiary propargyl alcohols, wherein preferably
R1 represents a saturated or unsaturated, branched or unbranched C1 to C20- alkyl, aryl, or arylalkyl,
R2 represents C1 to C4 alkyl, in particular methyl.
Examples of suitable propargyl alcohols which may be mentioned are:
3-methyl-1-butyn-3-ol,
3,7-dimethyl-6-octen-1-yn-3-ol (dehydrolinalool)
3,7-dimethyl-5-octen-1-yn-3-ol
3,7-dimethyl-4-octen-1-yn-3-ol
3,7-dimethyl-1-octyn-3-ol (hydrodehydrolinalool)
3,7,11-trimethyl-6,10-dodecadien-1-yn-3-ol (dehydronerolidol)
3,7,11-trimethyl-6-dodecen-1-yn-3-ol
3,7,11-trimethyl-1-dodecyn-3-ol (hydrodehydronerolidol)
1-ethynyl-1-cyclohexanol,
1-ethynyl-2,2,6-trimethyl-1-cyclohexanol
Possible alkenyl alkyl ethers of the formula III are preferably compounds in which
R4 represents hydrogen or methyl,
R5 represents hydrogen or methyl,
R6 represents methyl, ethyl, propyl, isopropyl, isobutyl or tert-butyl.
Examples of suitable alkenyl ethers which may be mentioned are:
isopropenyl methyl ether, isopropenyl ethyl ether, isopropenyl propyl ether, isopropenyl butyl ether, isopropenyl isobutyl ether, isobutyl isopropenyl ether, diisopropenyl ether, isopropenyl phenyl ether, 2-methoxy-1-butene, 2-ethoxy-1-butene, 2-propoxy-1-butene, 3-butoxy-1-butene, 2-methoxy-2-butene, 2-ethoxy-2-butene, 2-methoxy-1-pentene, 2-ethoxy-1-pentene, 2-methoxy-2-pentene, 2-ethoxy-2-pentene, 3-methoxy-3-pentene, 3-ethoxy-2-pentene, in particular isopropenyl methyl ether, isopropenyl ethyl ether and isopropenyl isopropyl ether.
Examples of suitable aliphatic sulfonic acids which may be mentioned are:
methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, halogen-substituted methanesulfonic acid, fluorosulfonic acid and cyclohexanesulfonic acid, in particular methane- and ethanesulfonic acid.
Examples of suitable sulfonic acid salts which may be mentioned are:
pyridinium p-toluenesulfonate, tetramethylammonium p-toluenesulfonate, pyridinium methanesulfonate, pyridinium ethanesulfonate, in particular pyridinium p-toluenesulfonate.
The sulfonic acids and the sulfonic acid salts mentioned can be either employed directly or prepared in situ via the corresponding sulfonic acid chlorides or anhydrides in a known manner.
The reaction is expediently carried out at temperatures between about 40xc2x0 C. and 200xc2x0 C., preferably between about 50xc2x0 C. and 120xc2x0 C.
The reaction can be carried out under normal pressure, but also under pressure. In a reaction under pressure, the reaction takes place in a pressure range from 1 to 100 bar, preferably 1 to 20 bar. The process can also be carried out as follows: In a 1st stage in the atmosphere and then the 2nd stage under increased pressure.
The molar ratio between the tertiary alcohol of the general formula II and the alkenyl alkyl ether of the general formula III in the process according to the invention is in general between 1:2 to 1:10, preferably between 1:2 to 1:3. In a reaction without a solvent, the excess alkenyl alkyl ether serves as the solvent and can be recovered by distillation when the reaction has ended.
The Saucy-Marbet reaction can be carried out with or without a solvent. Suitable solvents which can be employed in the context of the present invention are hydrocarbons, e.g. hexane, heptane, octane, toluene, and xylene, or ketones and ethers, e.g. isobutyl methyl ketone, diethyl ketone, isophorone or dimethoxypropane.
For carrying out the process, a procedure is in general followed in which either a mixture of the tertiary propargyl alcohol and the alkenyl alkyl ether is initially introduced into the reaction vessel and the catalyst is added either continuously or in portions in the form of a solid, a melt or, in particular, as a solution in a suitable solvent. Thereafter, the mixture is heated up to the reaction temperature. The acid catalyst can be initially introduced with the reactants or metered into the mixture in portions during the reaction.
The reaction can be carried out discontinuously, but also continuously.
The product formed, the 4,5-allene ketone, can be either isolated directly or converted by basic isomerization in a manner known per se (see U.S. Pat. No. 3,029,287) into a 3,5-dienone of the general form 
in which R1, R2, R3 and R4 have the abovementioned meaning;
the latter can be used as important intermediate stages for vitamin A, E, K1 and carotenoids.
However, the 4,5-allene ketones formed can also be hydrogenated in a manner known per se (R. Marbet and G. Saucy, Helv. Chim. Acta (1967),50; 1158-1167) to give saturated ketones 
in which R1, R2, R3 and R4 have the abovementioned meaning.
The saturated ketones can be important intermediate products for vitamin E synthesis.
The following examples illustrate the invention. The propargyl alcohols employed are described in U.S. Pat. No. 3,029,287 which is relied on and incorporated herein by reference.